Phytoplankton is a sentinel of ecosystem change in marine ecosystems. Composed by many species with different life-history strategies, it rapidly responds to environment changes. An analysis of time-series of the abundance of 54 phytoplankton taxa in Galicia (NW Spain) between 1989 and 2008 to determine the main trends in relation to climate and upwelling showed that most of their variability was stochastic, as seasonality and long term trends accounted for a minor fraction of the series. All trends were non linear, and taxa clustered in 4 groups according to the trend pattern but there was no defined pattern for diatoms, dinoflagellates or flagellates. No clear trend was shown by 23 taxa, 14 taxa decreased and 4 taxa increased during the early 1990s, while only 13 taxa showed a general increase through the series. In contrast, series of local environmental conditions (temperature, stratification, nutrients) and climate-related variables (atmospheric pressure indices, upwelling winds) showed a high fraction of their variability in deterministic seasonality and trends. As a result, each taxa showed independent responses to environmental and climate variablity, measured by generalized additive models. Most taxa showed a positive relationship with nutrient concentrations but only a few showed a direct relationship with stratification and upwelling. Climate variables only had measurable effects on some taxa but no common response emerged. Because its adaptation to frequent disturbances, phytoplankton communities in upwelling ecosystems appear less sensitive to changes in regional climate than communities characterised by short and well defined productive periods.IEO RADIALE
